PURPOSE:To obtain a metal thin film type magnetic recording medium having excellent weather resistance and durability under various environmental conditions of a wide range by providing a ferromagnetic metal thin film magnetic layer the surface of which is treated with halide of oxo acid having substd. or unsubstd. hydrocarbon group on a nonmagnetic supporting body. CONSTITUTION:The magnetic recording medium has a ferromagnetic metal thin film magnetic layer on a nonmagnetic supporting body and the surface of the magnetic layer is treated with halide of oxo acid having substd. or unsubstd. hydrocarbon group to form a strong protective layer comprising substd. or unsubstd. hydrocarbon on the surface of the magnetic layer. This protective layer protects the metal thin film magnetic layer and improves weather resistance and traveling durability of the medium. The halide of oxo acid modifies the metal thin film surface and adheres thereon to form an extremely strong surface-treated layer which has large protective effect for the magnetic layer. Thus, the medium has excellent weather resistance and durability under various environmental conditions of a wide range.